Image: Courtesy of Roderick MacKinnon
 MAPPING THE PATH: The transmembrane pore of K+ channels is composed of four identical subunits, of which two are shown. The ion pathway contains a narrow selectivity filter (yellow) and a wide central cavity (asterisk). Three helical elements include the outer helix (M1), pore helix (P), and inner helix (M2). The gate is formed by the inner helix Bundle. (Reprinted with permission from Nature © 2002)

Underlying every thought, heartbeat and movement are ion channels, busily conducting high-speed streams of ions into cells, like subway trains coursing through tunnels. Ion channels span the cellular membrane, forming passageways, or pores, through which ions flow down electrochemical gradients. Despite extensive studies of ion channels dating back more than 50 years, crucial structural pieces of the puzzle were still missing that would explain how the high-throughput transmission of ions is achieved, how channels discriminate between ions, and...

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